In this paper, the theoretical foundations of the equivalence between waveguide propagation below cutoff and artificial plasmas are carefully analyzed through the derivation of the propagation constants of normal modes in waveguides filled with anisotropic plasmas. The equivalence between waveguide and dielectric plasma proposed by Marquees et al., which is valid for evanescent TE modes, has a dual counterpart for magnetic plasmas and evanescent TM modes. This new equivalence states that a negative magnetic permeability medium can be simulated by means of TM modes below their cutoff frequencies. The need of an anisotropic filling of the waveguide for the equivalence between plasmas and evanescent modes is also highlighted. To exemplify the applicability of this new equivalence, a structure that implements a double-negative medium has been proposed. Full-wave simulations of the proposed structure and measurements from an experimental setup are presented, both of which corroborate the new equivalence's validity.

In this work, an optimized broadband method using multilayer transmission lines to characterize dielectric permittivity and loss tangent of material samples is presented. For this purpose, a microstrip line loaded with a piece of the selected dielectric to be characterized is used. From two-port measurements, and using different length lines, the propagation constant can be obtained. To minimize random errors and to improve the accuracy, an overdetermination of the method increasing the number of lines measured and a criterion to choose the optimal line lengths is considered. First, the measurement method itself is applied to uncovered microstrip lines and an accurate model of the substrate is obtained. Second, the lines are covered with several materials, made by fused deposition modeling (FDM) additive manufacturing technique, such as acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), high impact polystyrene (HIPS), thermoplastic polyurethane (TPU), copolyester (CPE), FLEX, polyethylene terephthalate glycol (PETG), and nylon. A model of the transmission line considering the cover is developed, and an electromagnetic (EM) simulator is used to indirectly determine the cover material electrical parameters. Results show excellent agreement with EM simulations in the 0.1-67-GHz frequency band, so they assess the suitability of the proposed method.

We present a three-section quadrature hybrid based on slot-coupled directional couplers, which operates over a bandwidth from 3.1 to 10.6 GHz. A prototype has been fabricated which exhibits a return loss better than 20 dB, isolation around 20 dB, an amplitude imbalance between output ports of less than plusmn0.75 dB and a phase imbalance between +1^deg and -3^deg across the 3.1-10.6 GHz band. This design outperforms previously reported results for ultra wide band operation.

Transmission-line transformers are devices used to match RF and microwave devices, to make the conversion balanced-unbalanced, or both things simultaneously. Transmission-line transformers are mandatory at frequencies where traditional magnetic coupling transformers do not operate properly. In this paper, a procedure to design transmission-line transformers with different configurations is presented. The procedure is based on the theoretical analysis of the device and has been validated via experimental study.

This paper demonstrates an ultra-light weight microwave rotary vane attenuator (RVA) manufactured using polymer-based 3-D printing. In addition, for the first time, conductive polylactic acid (PLA) is rigorously characterized across both X- and Ku-bands (8 to 18 GHz); while acrylonitrile butadiene-styrene (ABS) has similarly been characterized across Ku-band (12 to 18 GHz). Using the results from the conductive PLA characterization process, an electromagnetic model was created for predicting the performance of the RVA. It is shown that, even with its complex internal geometrical features, a mix of both dielectric and conductive PLA building materials, an assembly of multiple parts and a mechanically rotating central section, our experimental proof-of-concept prototype RVA exhibits excellent measured performance across Ku-band. This tunable microwave control device represents a higher-level of functionality for additive manufacturing, when compared to a fixed (i.e., non-movable) 3-D printed structure, opening the way for other groups to routinely 3-D print custom microwave components and subsystems in the not too distant future.